1. Field of the Invention
The present invention relates to a control of automobile internal combustion engines, and is particularly concerned with an automatic control apparatus for an engine throttle valve which is capable of minimizing loads of a motor for controlling a position of the throttle valve.
2. Description of the Prior Art
As a control apparatus for internal combustion engine throttle valves, there known hitherto, for example, are "Control Apparatus for Internal Combustion Engine Throttle Valves" disclosed in Japanese Patent Publication No. 25853/1983 dated May 30, 1983 and "Valve Driving Device" disclosed in Japanese Patent Laid-Open No. 145867/1980 dated Nov. 13, 1980.
In such conventional apparatuses, a throttle valve is supported rotatably on a pipeline. A motor for driving the throttle valve is coupled direct to the throttle valve or connected thereto through a reduction gear. A return spring is provided on the throttle valve, and thus when a current is not carried to the motor, it is returned invariably to a position whereat an engine comes to idling. A position sensor for detecting an opening is provided on the throttle valve, and information on a current position of the throttle valve is obtained from the position sensor, thereby applying a correction to a position control of the motor.
Generally in an automobile internal combustion engine for which a fuel injection is carried out downstream of the throttle valve, viscous deposits stick on the throttle valve due to a fuel scum return, a backfire and the like, which are capable of clogging the throttle valve at a full-open position. In the conventional apparatuses, a torque of the return spring is loaded in addition to a torque for relieving the throttle valve from such a clogged state, and thus a heavy torque is required for the motor. To obtain a heavy torque, a reduction ratio will be increased normally; however, such a measure is defective to deteriorate an answerability. To provide an enlarged motor therefor is to increase the weight of the apparatus inevitably, which is, needless to say, inadvisable.